Color Vision Deficiency is present in a percentage of the human population. Certain tasks which rely on color can become more challenging for these people.
Computer workstation tasks are often highly color dependent. Consider, for example, web browsing. Web browsers may indicate a link that has been visited in one color, and a link that has not been visited in another color. A person who cannot distinguish between the two colors simply misses the cue.
Non-color cues, such as text icons, graphics and so on can be used in conjunction with the colored cues. This technique works well in web page design. Other interfaces, which are more intensely visual, often cannot use this technique.